Immigration Department says children spend average of 45 days in Pontville

"They're developmentally quite vulnerable at that age and it would be a much better situation if they could be in a community detention setting where it's a more normalised environment and they have some freedom to come and go," she said.

Ms Mitchell says some of the children have been hospitalised because of mental health issues.

Call for children to live in community

She says the Government should try to place the children into community detention or allow them to stay with relatives already in the community.

"There are host families within the Australian context that have put up their hand as I understand it to host young people, and also some of these young people have relatives in the Australian community," she said.

"And for [the children and relatives] it's very hard to understand why they can't live with them while their claims are processed."

Ms Mitchell admits there will still be issues with children kept in community-based detention.

"But I would say there's a lot more hope and opportunity for those children, and they are on a much better trajectory than those children that are in the detention facility," she said.

Immigration Minister Tony Burke has signed off on releases for 18 of the centre's detainees.

Ms Mitchell cited quotes from several children she met during her visit to Pontville last month.

"Even if you make this place heaven it is not enough for us because we feel like we are in a cage. We feel people see us like animals in a cage," one child said.

"We stay up all night and sleep all day. We don't want to go to school because it upsets us to see others free," said another.

"At school people stare and laugh at us which makes us feel sad," a third child said.

A fourth child said the detainees felt pressure from their families.

"At 3am if you come here you will see people walking around like crazy because they can't sleep," the child said. "They are going crazy so people cut themselves."

Former teen detainee likens Pontville to prison

A 16-year-old boy from Afghanistan who spent the past two months at Pontville has told AM conditions at the centre are like a prison.

He said he felt disappointed and hopeless when he was there.

"Mentally, it makes you crazy. You find a lot of problems in there. Please don't keep the boys a lot there - don't keep them long in detention centre," he said.

He says teenagers slept in bunk beds in dorms with 20 people in the room.

He says every teenager had a locker and staff also had a key so they could search the lockers.

"The second key, that copy key, [was with] the officer and every week they'd come and search the lockers," he said.

The teen says he would earn points by attending school, which he could use to buy things like phone cards or sweets from the canteen.

"If you go to school you get the points, if you don't, you don't get the points," he said.

A spokesman from the Department of Immigration says the point system exists across the network and that every detainee gets a weekly allocation of 25 points.

Detainees separated into classes with different teachers

Children inside the Pontville centre attend several schools in Hobart, but the Afghan boy told AM that asylum seekers are separated into separate classes with different teachers from their Australian counterparts.

The Immigration Department says it is working to integrate asylum seekers into the broader school community.

The Afghan teen is now living in the community in a group home with other asylum seekers.

"I'm feeling better because now I'm free. I can study, I'm going to proper school, and I can see my future, that it's very bright," he said.

The Immigration Department says the average amount of time that detainees spend at Pontville is 45 days.